Posted by JAC on 4/17/2009, 3:02 pm, in reply to "Tornado Watch - Houston"

MESOSCALE DISCUSSION 0501 NWS STORM PREDICTION CENTER NORMAN OK 0145 PM CDT FRI APR 17 2009 AREAS AFFECTED...PORTIONS SE TX. CONCERNING...TORNADO WATCH 160... VALID 171845Z - 172045Z THE SEVERE WEATHER THREAT FOR TORNADO WATCH 160 CONTINUES. THOSE PORTIONS OF THIS WW BENEATH AND AHEAD OF ONGOING MCS SHOULD BE CONTINUED FOR TIME BEING. SFC MESOANALYSIS SHOWS MARINE FRONT NOW QUASISTATIONARY FROM OFFSHORE SABINE PASS WNWWD ACROSS SRN GLS BAY AREA TO ITS INTERSECTION WITH CONVECTIVE COMPLEX OVER AUSTIN COUNTY. LOW LEVEL SHEAR IS FAVORABLE...AND WILL REMAIN SO...INVOF FRONTAL ZONE. STG LLJ OF 50-55 KT REMAINS EVIDENT IN HGX/LCH VWP...PERHAPS EXAGGERATED SOMEWHAT BY MOTION OF BIRDS/BUGS IN THAT LAYER...BASED ON SEMICIRCULAR ANNULUS OF REFLECTIVITY IN THAT LAYER FROM HGX RADAR AND COMPARISONS WITH PRE-STORM LDB PROFILER WINDS AND AREA RUC SOUNDINGS. STILL...45-50 KT FLOW IS LIKELY WITHIN APPROXIMATELY 1 KM AGL...KEEPING HODOGRAPHS ENLARGED AND 300-400 J/KG SRH IN THAT LAYER. THICKENING ANVIL CLOUD COVER HAS MITIGATED SFC HEATING...CONTRIBUTING TO TENDENCY OF SBCINH TO INCREASE EWD ACROSS WW AREA INTO LA...AND MAKING EWD EXTENT OF SVR THREAT MORE UNCERTAIN/CONDITIONAL. STILL...MODIFIED RUC SOUNDINGS SUGGEST 1000-1500 J/KG MLCAPE OVER AND JUST S OF FRONT. TORNADO POTENTIAL HAS BECOME MORE CONDITIONAL GIVEN INCREASED CINH AND MESSY STORM STRUCTURES...BUT DOES STILL EXIST...ESPECIALLY WHERE STORMS CROSS THROUGH FRONTAL ZONE. SVR POTENTIAL IS FCST TO DIMINISH WITH NWD EXTENT FROM FRONT AS INFLOW-LAYER PARCELS BECOME PROGRESSIVELY/GRADUALLY MORE ELEVATED...AND AS MUCAPE DECREASES. ..EDWARDS.. 04/17/2009